1. Field of the Invention
This invention relates to apparatus and methods for estimating the range or distance from a camera to various points in a three-dimensional scene being viewed by the camera. More particularly, this invention relates to range estimation utilizing a single camera system, an optical mask, and digital processing of the digital image data that is generated by the camera.
2. Description of the Prior Art
Prior inventions directed to estimating the range to various points in a scene, or to accomplishing related goals such as determining object contour or creating a three dimensional image of an object, commonly utilize two spaced apart views of an object, and then triangulate to determine range. Other two camera systems determine range by correlating the image shifting that is required to match the two images that are provided by two spaced apart cameras. Kidode et al., U.S. Pat. No. 4,573,191, is an example of such a system. Marks et al., U.S. Pat. No. 4,178,090, is a variation which uses an exterior means to split an image, then present the split image to a single camera, and then record both images on a common piece of film.
Devices which do not require the use of two object views, or two cameras, include Greivenkamp, Jr., U.S. Pat. No. 4,794,550, which discloses enhancement of Moire contouring past the Nyquist frequency limit by utilizing a prior knowledge about the surface of the object being viewed. Desjardins et al., U.S. Pat. No. 4,825,263, discloses a method for determining object contours by shining a grid of light on the object and photographing the resulting reflection. Image processing then detects grid intersection points, and thereby determines surface curvature of the object. Steinpichler et al., U.S. Pat. No. 4,843,631, discloses a method of pattern recognition utilizing a comparison of the Fourier transform of an image to reference patterns. Uesugi et al., U.S. Pat. No. 5,102,223, discloses illuminating an object with a moving slit beam and comparing the image thus generated with a reference image to measure object curvature.
"Conoscopic holography, 1. Basic principles and physical basis", J. Opt. Soc. Am. A/Vol 9, No. 1/January 1992, by Gabrial Y. Sirat discloses a system to estimate the range to an object by utilizing a pair of polarized crystals which produce an image which is a monotonic function of misfocus to the object. The system measures only one distance within the scene.
The need remains in the art for a passive single camera range estimation system that directly measures range to various points in a scene.